The invention concerns a cage for cylindrical rolling elements, particularly needle rollers, said cage being rolled out of a sheet metal strip and comprising two side rings that are connected by profiled crossbars that form pockets, said crossbars comprising sections that are situated inside of a pitch circle and, parallel to said sections, further sections that are situated outside of the pitch circle, said sections and said further sections being connected to one another by still further sections that are inclined to a cage axis.
A cage of the pre-cited type is known from the document DE-OS 21 47 170 and is made by a method in which a flat sheet metal strip is worked into the desired cross-sectional profile by rolling, the pockets for lodging the rolling elements are punched out either before or after the profiling step, and finally, the strip is bent into a circular shape, whereafter, if required, its free ends are welded together. In such thin-walled profiled and bent M- or W-shaped cages, the rolling elements are retained by retaining edges arranged inside or outside the pitch circle. The cages are made of thin-walled sheet metal because its very small wall thickness permits a particularly economic fabrication of the pockets by punching.
This, however, has the drawback that punching tears and generally rough punched surfaces are formed on the crossbars i.e., the guide surfaces for the rolling elements are rough and inexact on the whole. But rough crossbar surfaces on which the needle rollers run lead to abrasion. Inexact crossbar surfaces, in their turn, lead to an axial displacement and an axial contact of the cage end faces against the axial boundary surfaces of the bearing with considerable surface pressure. In the case of idler pulley bearings in mechanical transmissions, this can result in considerable transverse and displacing forces acting on the idler pulley bearing and make the bearings tend to wobbling movements. Another drawback results from punching out the pockets before bending the cage strip into a round shape. In the finished cage, the pockets then have a V-shaped profile in the direction of the bearing center so that there is the danger of the rolling elements getting clamped.
Starting from this prior art, an attempt has been made in DE 197 40 435 A1 to avoid the aforesaid drawback viz., that the cage pockets for lodging the needle rollers have a V-shaped configuration in the finished, bent state of the cage. The procedure used is that, after the pockets have been punched out, an additional shaping step, known to the person skilled in the art under the name of stamping, is carried out in which, by a displacement of material, the cage pockets are pressed into the shape required for its precise functioning. This means, in the first place, that the rolling elements bear against the cage crossbars in the region of the pitch circle and not, as was hitherto the case, inside or outside the pitch circle. By virtue of this guidance in the region of the pitch circle, that is obtained through parallel guiding surfaces of the pockets, the undesired transverse and displacing forces on the cage are avoided.
A drawback of this is that the improved function of the cage is obtained only at the price of carrying out an additional work step, the so-called stamping. Stamping is effected in that each individual crossbar of a cage is loaded on both sides with two tong-like stamping tools using a force that produces a material displacement in the crossbar region. It is quite obvious that such a fabrication technology is very complex and expensive due to the separate working of each individual crossbar.
It is an object of the invention to improve a generic cage of the pre-cited type so that its excellent running properties i.e., the rolling contact of the rolling elements in the region of the pitch circle, can be obtained during the fabrication process even without an additional work step.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that in the profiled, punched and unbent state of the sheet metal strip, the pockets, as seen in a top view, have a curved shape in the region of the inclined sections, so that an axially inner, first convex curve B1 merges into an outer, second concave curve B2.
Due to the adapted pocket geometry of the invention i.e., the special configuration of the crossbars in the profile transition between sections situated inside and outside the pitch circle, it is achieved that in the finished, bent state, the pocket flank in the profile transition is radially parallel to the center of the pocket and axially parallel to the rolling element. This means that the rolling elements run against the individual crossbars of the cage within the pitch circle region. Because, as taught by the invention, this pocket geometry is obtained solely by punching i.e., without the stamping step hitherto required in the prior art, a cage of this type can be made much faster and at substantially lower cost. The separation, known per se, between the outer and inner retention of the rolling elements on the one hand, and the contact region of the rolling elements on the cage, on the other hand, is obtained for the first time simply and solely by the pocket geometry produced by punching, in combination with bending round the cage strip to form the finished cage. This means that the pocket geometry in the flat strip must be configured so that, after the strip is bent round, the rolling elements contact the cage in the region of the pitch circle.
Advantageous features of the invention will be described below.
According to a first advantageous feature, the cage has an M-shaped configuration which means that the sections of the cage starting from the side rings and extending parallel to the cage axis are arranged outside the pitch circle. If according to another feature, the cage has a W-shaped configuration, the sections of the cage starting from the side rings and extending parallel to the cage axis are arranged inside the pitch circle.
According to further features of the invention, the cage can be guided on the outside, on the inside or on the rolling elements. Finally, according to still other features of the invention, the cage can be used in a crank pin or in a planet gear bearing. Due to the high speeds of rotation in these cases of use, large forces act on the cage so that precisely functioning bearing cages are an indispensable requirement.
Advantageously, the starting material for making the cage is an endless strip that after reaching the desired strip thickness, is appropriately profiled for obtaining the desired, later cage shape. After the cage strip has been profiled, the pockets are punched out and the strip is bent into a round cage shape, whereafter, if necessary, the cage ends are welded together. Cutting to length of individual cage strips to correspond to the desired size of the finished cage can be done before or after profiling or even after the pockets have been punched out.
The invention will now be described more closely with reference to the example of embodiment illustrated in the appended drawings.